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fixes for at-view and at-views #20247

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Jan 27, 2017
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fixes for at-view and at-views #20247

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f225d82
fix hygiene and side-effects problems in at-view
stevengj Jan 26, 2017
7aa23e0
fix various problems with at-views macro
stevengj Jan 26, 2017
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94 changes: 73 additions & 21 deletions base/subarray.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -333,25 +333,32 @@ should transform to
A[B[endof(B)]]

"""
function replace_ref_end!(ex,withex=nothing)
replace_ref_end!(ex) = replace_ref_end_!(ex, nothing)[1]
# replace_ref_end_!(ex,withex) returns (new ex, whether withex was used)
function replace_ref_end_!(ex, withex)
used_withex = false
if isa(ex,Symbol) && ex == :end
withex === nothing && error("Invalid use of end")
return withex
return withex, true
elseif isa(ex,Expr)
if ex.head == :ref
S = ex.args[1] = replace_ref_end!(ex.args[1],withex)
ex.args[1], used_withex = replace_ref_end_!(ex.args[1],withex)
S = isa(ex.args[1],Symbol) ? ex.args[1]::Symbol : gensym(:S) # temp var to cache ex.args[1] if needed
used_S = false # whether we actually need S
# new :ref, so redefine withex
nargs = length(ex.args)-1
if nargs == 0
return ex
return ex, used_withex
elseif nargs == 1
# replace with endof(S)
ex.args[2] = replace_ref_end!(ex.args[2],:(Base.endof($S)))
ex.args[2], used_S = replace_ref_end_!(ex.args[2],:($endof($S)))
else
n = 1
J = endof(ex.args)
for j = 2:J-1
exj = ex.args[j] = replace_ref_end!(ex.args[j],:(Base.size($S,$n)))
exj, used = replace_ref_end_!(ex.args[j],:($size($S,$n)))
used_S |= used
ex.args[j] = exj
if isa(exj,Expr) && exj.head == :...
# splatted object
exjs = exj.args[1]
Expand All @@ -364,16 +371,23 @@ function replace_ref_end!(ex,withex=nothing)
n += 1
end
end
ex.args[J] = replace_ref_end!(ex.args[J],:(Base.trailingsize($S,$n)))
ex.args[J], used = replace_ref_end_!(ex.args[J],:($trailingsize($S,$n)))
used_S |= used
end
if used_S && S !== ex.args[1]
S0 = ex.args[1]
ex.args[1] = S
ex = Expr(:let, ex, :($S = $S0))
end
else
# recursive search
for i = eachindex(ex.args)
ex.args[i] = replace_ref_end!(ex.args[i],withex)
ex.args[i], used = replace_ref_end_!(ex.args[i],withex)
used_withex |= used
end
end
end
ex
ex, used_withex
end

"""
Expand All @@ -385,9 +399,15 @@ an assignment (e.g. `@view(A[1,2:end]) = ...`). See also [`@views`](@ref)
to switch an entire block of code to use views for slicing.
"""
macro view(ex)
if isa(ex, Expr) && ex.head == :ref
if Meta.isexpr(ex, :ref)
ex = replace_ref_end!(ex)
Expr(:&&, true, esc(Expr(:call,:(Base.view),ex.args...)))
if Meta.isexpr(ex, :ref)
ex = Expr(:call, view, ex.args...)
else # ex replaced by let ...; foo[...]; end
assert(Meta.isexpr(ex, :let) && Meta.isexpr(ex.args[1], :ref))
ex.args[1] = Expr(:call, view, ex.args[1].args...)
end
Expr(:&&, true, esc(ex))
else
throw(ArgumentError("Invalid use of @view macro: argument must be a reference expression A[...]."))
end
Expand All @@ -404,21 +424,53 @@ end
@propagate_inbounds maybeview(A) = getindex(A)
@propagate_inbounds maybeview(A::AbstractArray) = getindex(A)

# _views implements the transformation for the @views macro.
# @views calls esc(_views(...)) to work around #20241,
# so any function calls we insert (to maybeview, or to
# size and endof in replace_ref_end!) must be interpolated
# as values rather than as symbols to ensure that they are called
# from Base rather than from the caller's scope.
_views(x) = x
_views(x::Symbol) = esc(x)
function _views(ex::Expr)
if ex.head in (:(=), :(.=))
# don't use view on the lhs of an assignment
Expr(ex.head, esc(ex.args[1]), _views(ex.args[2]))
# don't use view for ref on the lhs of an assignment,
# but still use views for the args of the ref:
lhs = ex.args[1]
Expr(ex.head, Meta.isexpr(lhs, :ref) ?
Expr(:ref, _views.(lhs.args)...) : _views(lhs),
_views(ex.args[2]))
elseif ex.head == :ref
ex = replace_ref_end!(ex)
Expr(:call, :maybeview, _views.(ex.args)...)
Expr(:call, maybeview, _views.(ex.args)...)
else
h = string(ex.head)
if last(h) == '='
# don't use view on the lhs of an op-assignment
Expr(first(h) == '.' ? :(.=) : :(=), esc(ex.args[1]),
Expr(:call, esc(Symbol(h[1:end-1])), _views.(ex.args)...))
# don't use view on the lhs of an op-assignment a[i...] += ...
if last(h) == '=' && Meta.isexpr(ex.args[1], :ref)
lhs = ex.args[1]

# temp vars to avoid recomputing a and i,
# which will be assigned in a let block:
a = gensym(:a)
i = [gensym(:i) for k = 1:length(lhs.args)-1]

# for splatted indices like a[i, j...], we need to
# splat the corresponding temp var.
I = similar(i, Any)
for k = 1:length(i)
if Meta.isexpr(lhs.args[k+1], :...)
I[k] = Expr(:..., i[k])
lhs.args[k+1] = lhs.args[k+1].args[1] # unsplat
else
I[k] = i[k]
end
end

Expr(:let,
Expr(first(h) == '.' ? :(.=) : :(=), :($a[$(I...)]),
Expr(:call, Symbol(h[1:end-1]),
:($maybeview($a, $(I...))),
_views.(ex.args[2:end])...)),
:($a = $(_views(lhs.args[1]))),
[:($(i[k]) = $(_views(lhs.args[k+1]))) for k=1:length(i)]...)
else
Expr(ex.head, _views.(ex.args)...)
end
Expand All @@ -439,5 +491,5 @@ that appear explicitly in the given `expression`, not array slicing that
occurs in functions called by that code.
"""
macro views(x)
_views(x)
esc(_views(replace_ref_end!(x)))
end
23 changes: 18 additions & 5 deletions test/subarray.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -473,8 +473,6 @@ end
@test collect(view(view(reshape(1:13^3, 13, 13, 13), 3:7, 6:6, :), 1:2:5, :, 1:2:5)) ==
cat(3,[68,70,72],[406,408,410],[744,746,748])



# tests @view (and replace_ref_end!)
X = reshape(1:24,2,3,4)
Y = 4:-1:1
Expand All @@ -494,10 +492,16 @@ u = (1,2:3)
@test X[(1,)...,(2,)...,2:end] == @view X[(1,)...,(2,)...,2:end]

# test macro hygiene
let size=(x,y)-> error("should not happen")
let size=(x,y)-> error("should not happen"), Base=nothing
@test X[1:end,2,2] == @view X[1:end,2,2]
end

# test that side effects occur only once
let foo = [X]
@test X[2:end-1] == @view (push!(foo,X)[1])[2:end-1]
@test foo == [X, X]
end

# test @views macro
@views let f!(x) = x[1:end-1] .+= x[2:end].^2
x = [1,2,3,4]
Expand All @@ -512,6 +516,16 @@ end
@test x == [5,6,19,4]
f!(x[3:end])
@test x == [5,6,35,4]
x[Y[2:3]] .= 7:8
@test x == [5,8,7,4]
x[(3,)..., ()...] .+= 3
@test x == [5,8,10,4]
i = Int[]
# test that lhs expressions in update operations are evaluated only once:
x[push!(i,4)[1]] += 5
@test x == [5,8,10,9] && i == [4]
x[push!(i,3)[end]] += 2
@test x == [5,8,12,9] && i == [4,3]
end
@views @test isa(X[1:3], SubArray)
@test X[1:end] == @views X[1:end]
Expand All @@ -523,9 +537,8 @@ end
@test X[1:end,2,Y[2:end]] == @views X[1:end,2,Y[2:end]]
@test X[u...,2:end] == @views X[u...,2:end]
@test X[(1,)...,(2,)...,2:end] == @views X[(1,)...,(2,)...,2:end]

# test macro hygiene
let size=(x,y)-> error("should not happen")
let size=(x,y)-> error("should not happen"), Base=nothing
@test X[1:end,2,2] == @views X[1:end,2,2]
end

Expand Down